Automatic steering systems have been designed for agricultural vehicles. Such systems utilize crop row sensors that feel the crop stalks and determine appropriate steering actions for the vehicle based on the feedback from these row sensors. For example, U.S. Pat. No. 7,716,905, issued to Wilcox et al. in 2010, and assigned to the assignee of the present application, describes a sensing assembly for detecting plants or plant stalks in a crop row. This assembly includes a movable arm which interacts with plants standing in a field and a sensor which generates a signal depending on the position of the movable arm.
Another known crop row sensor includes a long rubber bar or paddle. A magnet is attached to the paddle. When the paddle touches a crop stalk, it bends as the stalk pushes the tip of the paddle backwards. The amount that the paddle bends backwards is measured with a Hall-Effect sensor which senses a magnetic field produced by the magnet. The sensor voltage increases as the paddle is bent further back, so that the sensor voltage represents the position of the crop row relative to the vehicle. When the paddle is straight (not bent back), the sensor voltage is very low and this is interpreted as missing or absent crop.
Occasionally, there are gaps or absences of stalks in a crop row. In some cases these gaps can be fairly long (10-20 ft). During these gaps, the steering system must determine what action is appropriate as soon as possible in order to keep the vehicle properly aligned with the crop row.
When the paddle has been pushed back and then reaches a space where there is a gap in the row (no plants), the rubber paddle will “bounce” forward and oscillate for a few seconds until it settles completely in the relaxed straight position. This bouncing of the rubber paddle produces an oscillating sensor voltage. This oscillating voltage is interpreted as indicating that there is a gap in the crop row. Previously, it could be determined that a crop gap existed only ½ to 3 seconds after the start of a bouncing event. During this time, the machine does not steer effectively to remain on the row. This is because at typical corn harvesting speeds of 4 to 6 miles per hour, 5 to 9 feet of distance is covered per second. It is desired to detect a bouncing event more quickly so that the vehicle can be steered more accurately while it is motion.